Among the techniques currently employed in connection with dilatation of a body lumen, such as a blood vessel that has become restricted by pathological or traumatic occurrence, has been to place an endovascular stent within the dilated region of the vessel, in order to maintain the vessel patient. One technique for placing such an endovascular stent has been to mount the stent onto a folded balloon of a balloon catheter and then insert and advance the stent and catheter together into the body lumen to locate the stent at the intended site of implantation. So located, the balloon then is inflated to expand the stent into engagement with the vessel wall to stabilize the position of the stent within the lumen. The procedure requires first that the stent be properly located on the balloon and second, that it be secured to the balloon to assure it will remain in place during the placement procedure.
Positioning the stent on the balloon has involved selection of a stent having an initial internal diameter greater than the radial dimensions of the folded balloon and the catheter to enable the stent to be slipped over the catheter and about the balloon. The stent then is constricted radially about the balloon and catheter by means of pincers or other crimping tools to inelastically deform the stent to a smaller diameter in which the stent maintains a firm grip on the folded balloon.
The foregoing technique for securing an endovascular stent to the balloon of the catheter presents a number of difficulties. The balloon typically is formed from a very thin, membranous material that is susceptible to damage, either by the stent rubbing against the folds of the balloon when the stent is positioned along the balloon or by excessive crimping pressure when the stent is constricted tightly about the balloon. Crimping the stent onto the balloon necessarily is empirical and difficult to control. Additionally, some stents are formed employing a laser cutting procedure in which edges of the stent may be insufficiently rounded thereby presenting increased risk of damage when crimped about the balloon. Moreover, once the stent is crimped onto the balloon it may not be possible to detect the presence of such damage. Consequently, there may be increased risk that the balloon will burst during inflation with potentially life threatening consequences to the patient.
Also, among the difficulties with the above-described technique for mounting a stent onto a balloon catheter is that because of the uncertainties in the use of the crimping technique, the stability of the position of the stent on the balloon may be compromised. When a catheter is advanced along a body lumen it can be expected to encounter deviations, bends, or restrictions resulting either from the natural anatomy of the lumen or by the presence of atherosclerotic plaque, any of which may cause the stent to slip from its initial position on the balloon. Additionally, the shifting of the stent on the balloon may result in the stent snagging the balloon, causing undetected damage that, in turn, can present difficulties in localizing and stabilizing the stent at its intended placement site. Even if slipping of the stent on the balloon is detected, it can be expected to further lengthen the duration of the procedure. Most seriously, the stent possibly could become irretrievably separated from the balloon inside the patient's body, thereby presenting significant risk to the patient.